The present invention generally relates to an electro-hydraulic hitch control system for controlling a hitch mounted on an agricultural tractor, and more particularly, relates to a method of calibrating a control parameter of such a hitch control system.
Currently available hitch control systems have various parameters which must be determined or calibrated and stored in order for the hitch control system to function as desired.
For example, U.S. Pat. No. 5,012,415, issued to Boe et al., in 1991 describes a hitch control system raise rate calibration method which requires the operator to manipulate the hitch control lever and a drop rate potentiometer.
U.S. Pat. No. 4,931,967, issued to Boe et al., in 1990 describes a hitch control system having a calibration and configuration algorithm which operates to establish the sensor ranges of all sensors installed and disables certain configurable features if the associated sensors are not present.
U.S. Pat. No. 5,472,056, issued to Orbach in 1995 describes a hitch assembly and control system and calibration methods therefore. The calibration methods determine and store calibration parameters relating to lower hitch position, upper hitch position, hitch lower threshold and hitch raise threshold.
U.S. Pat. No. 5,918,195, issued to Halgrimson et al., in 1999, describes a system for calibrating a control system command device by moving the command device into predefined positions and storing sensed calibration values.
U.S. Pat. No. 5,810,095, issued to Orbach et al., in 1998, describes a hitch control system wherein valve control signal threshold values are modified in response to detection of undesired hitch movement.
But, none of the systems or methods described in these patents provides any system or method for determining hitch raise rate calibration parameters.
For prior production of John Deere tractor hitch control systems, the hitch raise rate calibration parameter was experimentally determined. In particular, a small group of sample tractors having different combinations of hitch cylinder sizes and raise valves was chosen. For each sample tractor, a range of different raise valve currents was tested to determine what raise valve current would cause the hitch to fully raise in 3 seconds. An average number was determined for groups of vehicles with the same cylinder size and raise valve. A lookup table of these numbers and the corresponding cylinder sizes and valves was stored in the hitch control units on the tractors. Then, during the manufacturing process of each tractor, a technician selected and entered into the hitch control unit data for the cylinder and valve for that particular tractor, and the hitch control unit then selected or enabled and used the corresponding valve raise rate current. However, it was time consuming to test multiple different experimental raise current values. Also, the experimentally determined average number may not produce the desired raise rate for a particular tractor. Also, the technician may enter incorrect data pertaining to cylinder size and valve.
If the raise rate calibration value is determined during field operation, inaccuracies may be caused by varying conditions and limitations on the number of changes allowed to the available nonvolatile memory hardware. For example, the system may set the calibration value artificially high due to low engine speed or other conditions. Then, when these conditions are adjusted or removed, the hitch will raise at an excessive rate for a moment with a rapid deceleration as the control system adjusts to these new conditions. Such changes in acceleration can cause excessive jerk that can cause customer dissatisfaction.